Page 9 - дисертація Головчук

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austenite, which has lower microhardness than high-carbon martensite. It was

observed that much more carbon was burned out from little drops formed from PW

of smaller diameter, and therefore the content of austenite in the lamellae was lower,

and martensite one was accordingly higher.

The adhesion of coatings (martensite with boride inclusions) made of

50CrNi25MnSi PW and 250Cr21WVMnSi PW (especially with PW of larger

diameter) decreased slightly with thickness increase of the lamellae in the coating

structure. This is due to the tensile stresses, under the influence of which there were

single microcracks or their network in the sprayed coatings, which significantly

reduced the adhesion of the coatings to the steel base. For the coating (martensitic

class) made of 50Cr6Mn2MoSi PW, the inverse pattern was found. The adhesion of

the coating (martensitic class) to the steel base increases with diameter of the PW

and the thickness of the lamellae in its structure. This was explained by the higher

thermal energy of the drops, the lower carbon burn and the formation of coatings

with the matrix phase of high-carbon martensite. The more carbon in the martensite,

the lower the coefficient of thermal expansion of the coating can be observed that

causes lower residual tensile stresses.

Abrasive wear-resistance of coatings (ustenite of carbide class), sprayed from

250Cr21WVMnSi PW (especially ones of larger diameter), decreases with thickness

increase of the lamellae in their structure. This result was explained by the greater

amount of residual austenite in the coating, which has lower microhardness than

martensite. Smaller drops are characterized by higher carbon burn than larger ones.

Therefore, in the coating sprayed from PW with a diameter of 1.6 mm there is less

carbon than in the coating with a diameter of 2.4 mm, and hence it has less residual

austenite.

As the thickness of the lamellae in coatings (martensitic class with borides

inclusions) sprayed from 50CrNi25MnSi PW (especially ones of larger diameter)

increases, their abrasive wear- resistance increases as well. This is due to the increase

in the hardness of such coatings and the lower level of residual tensile stresses. Here,